1. Field of the Invention
The present invention relates to fluid pumps. More particularly, this invention relates to a medical irrigation fluid pump which is powered by a source of vacuum commonly available in an operating room.
2. State of the Art
Many medical procedures require the delivery of fluid under pressure or the pumping of fluid from a container through a conduit. Typical among these procedures are those which require irrigation of a surgical site. Irrigation is the washing of the surgical site with a stream of sterile water or other sterile fluid irrigant. Irrigants are supplied in containers and are delivered to the surgical site through a conduit. The most commonly used technique for delivering irrigant to the surgical site is by gravity flow from an overhead supply. Irrigation bags containing sterile irrigant are hung at a height of about six to eight feet above the patient. A tube leading from the bags is connected to an irrigation cannula. The tube is typically provided with a clamp for controlling the flow of irrigant. Although this method seems relatively easy and inexpensive to implement, the fluid pressure of the irrigant applied to the surgical site is limited by the height of the irrigation bag. Unfortunately, many procedures require that the irrigant be delivered with significantly greater pressure than is possible with the simple gravity feed. In order to increase the pressure of the irrigant, an attending nurse may be required to squeeze the irrigation bag during the course of the procedure. Alternatively, a pressure cuff may be applied to the bag and pumped with pressure, and repumped when pressure drops. Moreover, even in procedures where the pressure of gravity feed is sufficient, it is usually necessary to change irrigation bags several times during a procedure. When the irrigation bags are located considerably above the patient, changing the bags can become complicated and tedious.
In order to overcome the disadvantages of gravity feed irrigation, several types of medical pumps have been proposed. Since most operation rooms are equipped with a source of compressed gas such as air or nitrogen and/or a source of vacuum, several attempts have been made to provide a pump which is driven by positive or negative pressure. U.S. Pat. Nos. 4,662,829 and 4,741,678 to Nehring disclose several types of pulsatile two-stroke pumps which include an elastic diaphragm driven by a pressure source and one pump which uses a cylindrical elastic sleeve driven by a vacuum source. The vacuum powered pump of Nehring consists of a cylindrical canister and an internal flexible elastic sleeve with an annular vacuum chamber between the canister and the sleeve. The ends of the sleeve are hermetically sealed to the inlet and outlet of the pump, and check valves are provided at the inlet and outlet to limit fluid flow in a respective direction into and out of the sleeve. The canister is provided with a fitting for connection to a vacuum source and a spring biased valve operated by a radially inward extending stem. According to Nehring, when vacuum is applied to the canister, the annular vacuum chamber is evacuated and the elastic sleeve expands. As the sleeve expands, negative pressure is induced in the sleeve which causes the inlet check valve to open, the outlet check valve to close, and fluid to flow into the sleeve. When the sleeve expands to a certain point, it contacts the stem of the valve and opens the valve allowing air to enter the vacuum chamber. As air enters the vacuum chamber, the sleeve compresses forcing the fluid out of the sleeve through the outlet check valve. When the sleeve compresses to the point where the valve closes, the cycle repeats.
While the vacuum powered pump of Nehring seems practical in concept, the cylindrical elastic sleeve does not operate well. The effective fluid pressure imparted by the sleeve is quite low and is well under one atmosphere. Nehring achieves relatively higher output pressure, however, with positive pressure pumps. The positive pressure pumps have a circular diaphragm which overlies a source of pressure and a pressure outlet port. A pumping chamber with fluid inlet and outlet ports overlies the diaphragm. Pressure from the source of compressed air or nitrogen causes the diaphragm to rise until the pressure outlet port is exposed whereupon the diaphragm falls until the pressure outlet port is closed. The rate of pumping and the fluid pressure output is determined by the change in volume of the pumping chamber due to expansion of the diaphragm, i.e. the "stroke" of the diaphragm. In order to assure the maximum fluid pressure, the dimensions and proportions of the diaphragm, the pressure port, and the outlet port must be carefully chosen. While the positive pressure pump of Nehring is more efficient than his vacuum powered pump, it is difficult to design, and it relies on a source of pressure which may not be available.
A somewhat better solution to a pressure driven pump is provided in U.S. Pat. No. 5,281,108 to Brooke which provides a pump which is similar to that of the Nehring pump, except that the pressure outlet port is provided with a valve which is biased shut and the diaphragm is connected to the valve with a "lost motion connection". This allows the diaphragm to expand significantly more than the diaphragm of the Nehring pump before the pressure outlet opens causing the diaphragm to collapse. That is, the diaphragm of the Brooke pump has a longer stroke than that of Nehring. Brooke, however, does not disclose a vacuum powered pump and it is not evident that the design of Brooke would be compatible with the use of a vacuum as a power source.
Several other pumps have been provided in the art, such as the pumps disclosed in U.S. Pat. No. 5,261,883 to Hood et al., but these pumps are not powered by a source of constant vacuum. They rely on a "fluidic driver" which provides a pulsed source of pressure or vacuum.